Disposable garments such as diapers, training pants, sanitary napkins, panty liners, and incontinent garments, and especially catamenial devices have been undergoing considerable modification which have reduced their thickness but has retained or improved their absorbency and ability to retain body exudates. For convenience in the description, a panty liner or a very thin absorbent pad used primarily for feminine hygiene which may be used for undergarment protection between menstrual periods as well as absorbing light flow between and during periods will be described herein.
Generally, a panty liner comprises: a liquid-pervious, body side cover which is comfortable to the wearer; an absorbent core, typically composed of a fibrous material capable of absorbing body exudates and which may be a natural or a synthetic material or a combination of both; and a liquid-impervious baffle. The baffle's periphery may be coincident with the cover and the absorbent core, but this is not required.
Usually, the backing is a polyethylene film having a thickness of about 0.001 to about 0.005 of an inch (0.025 to 0.13 millimeters). The construction of a panty liner generally provides for a pressure sensitive adhesive applied to the garment facing side of the baffle. The adhesive is of the type that is capable of securing the panty liner to the crotch portion of an undergarment, yet permitting removal of the panty liner when soiled. In applying a pressure-sensitive adhesive to the liquid-impermeable baffle, a common practice is to transfer coat the adhesive on a suitable substrate, such as a Kraft paper that is silicone coated.
A panty liner's thinness makes it very flexible, which allows the panty liner to wrinkle during use and fold at the line along the edges as the panty liner is arcuately bent. When the panty liner's entire periphery is compressed or compacted sufficiently to seal the edges, relatively harsh and sharp edges are formed which tend to be abrasive. In attempting to obviate this undesirable abrasive edge, foamed materials have been utilized as a baffle to form a softer edge. A difficulty arises in producing a panty liner that is both low in cost to manufacture and comfortable to the wearer. For the panty liner to be cost competitive, the foam must be thin but at the same time have a structural integrity to withstand the forces applied to the adhesive coated surface when the panty liner is removed or repositioned.
Polyolefin foams, and specifically a polyethylene foam, have a low surface energy rendering it difficult to obtain a good bonding of a garment adhesive to the foam material. The prior art describes a number of methods that have attempted to increase the bonding of adhesives to polyolefin surfaces. These techniques are time consuming, costly and generally ineffective for constructing panty liners. It must also be borne in mind that the garment adhesive is in a hot melt state and cannot be directly applied to the foam because the foam is far too heat sensitive.
In one method disclosed in the patent literature for applying a garment adhesive to a polyethylene foam the adhesive is mixed in a hydrocarbon carrier prior to its application on the foam. This method is impractical for products that intimately contact human skin because the hydrocarbon may cause skin irritations or other health risks. Additionally, using solvents as a carrier for applying adhesive requires massive ovens for removing the solvents, adding to the product's cost.
Other methods disclosed in the prior art have concentrated on improving the foam's surface characteristics, making it more receptive to adhesive bonding. These methods include corona or flame treatment of the foam prior to its contacting the adhesive and/or using various adhesive primers to enhance the bond.
Yet another method disclosed in the patent literature uses a double-faced pressure sensitive adhesive tape for securing a polyethylene foam backing to the clothing of a user. The tape has an adhesive coating applied to each surface. The adhesive level of the double-faced tape attached to the undergarment is less than the adhesive level of the side of the double-faced tape attached to the ethylene polymer containment backing. The literature also teaches that if the formulation of the adhesive is the same on both sides of the double-faced tape, when the release strip is removed it delaminates the adhesive from the foam backing, pulling the adhesive completely away from the foam rather than being completely released.
While the above methods have had limited success in their application with crosslinked polyolefin foams, it has been found that these methods are unsatisfactory for bonding an adhesive to a non-crosslinked polyethylene foam.
It is therefore desireable to transfer coat a substrate with an adhesive without having to cure the adhesive using ovens. It is also desirable to coat a garment adhesive onto a suitable substrate and then transfer coat the adhesive from the substrate to a polyolefin foam, and preferably a non-crosslinked foam, without having to pre-treat the foam surface using a corona or flame treatment or other surface modifiers.